1. Field of the Invention
The present invention relates to a method and apparatus in the form of a hydraulic unit for actuating a vehicle clutch.
2. Description of the Related Art
Solutions known heretofore for actuating a clutch in an axle drive of a vehicle, in order to compensate for a steering error in certain driving situations, provide for a hydraulic unit that includes a high-pressure storage device, which must be filled up to the maximum clutch pressure in order to be able to engage the clutch or clutches with rapid response in those certain driving conditions. However, a low pressure in the pressure storage device would be adequate for pre-filling a clutch.
FIG. 1 shows a schematic depiction of such a hydraulic unit, as it is used in the existing art.
A pump 1 is driven by an electric motor 2 and fills the high pressure storage device 3, which is designed as a diaphragm-type accumulator. A sensor 4 measures the pressure. If two clutches 5 and 6 are provided, they are each actuated via a solenoid valve 7 and 8, respectively, and if necessary are supplied with the working fluid from the high pressure storage device 3. The pump 1 is supplied with the working fluid from a tank 9.
The solenoid valves 7 and 8 are designed, for example, as pressure-reducing valves. To pre-fill the clutches 5 or 6 it would be adequate to transport the working fluid at a low pressure of, for example, 5 to 10 bar, in order to fill the lift free-play of the clutches. To engage the clutch 5 or 6 a pressure of about 45 bar would have to be present, without need of a flow volume of working fluid.
However, the known hydraulic unit uses a large and expensive high-pressure storage device to fill and to engage the clutches 5 or 6.
If the clutches 5 and 6 are disengaged, the working fluid flows through the solenoid valves 7 and 8 back into the tank 9. The depicted elements of the known hydraulic unit are connected with each other via hydraulic lines or control lines, as shown in FIG. 1.
By switching the solenoid valves 7 and 8 accordingly, the clutches 5 and 6 are supplied with working fluid from the high pressure storage device 3, so that they are engaged, or the working fluid is transported from the clutches 5 and 6 back into the tank 9, whereupon the clutches 5 or 6 disengage by their own weight or a spring.
An object of the present invention is therefore to provide a device in the form of a hydraulic unit and a method for actuating this device, which enables the filling and engaging of the at least one clutch with simple construction and while maintaining high dynamics (rapid response), while the intent is to dispense with the use of a high-pressure storage device.
Preferably, in this case two multi-plate clutches provided in a rear axle of a vehicle, i.e., in a rear axle differential, should be engaged hydraulically to redistribute the wheel torques.